1. Field of the Invention
The present invention relates to a seal ring which is used for sealing at adjoining junctions provided between flange joints of composite tanks, pipes made of fiber reinforced plastics, etc. and the flange joint covers, and a seal structure for flange joint for composite tanks and pipes which use said seal ring.
2. Description of the Related Arts
Lightweight, high-strength and carbon fiber reinforced plastic (CFRP) composite materials are widely used in aircraft to contain low temperature fluids in low temperature tanks and flange joints. Since such low temperature tanks and flange joints can contain very low temperature gases of approximately xe2x88x92250xc2x0 C., the fluid seals at the tank and at the flange joint with the flange joint cover must be able to maintain a tight seal without being affected by thermal contractions from the very low temperature gases.
FIG. 4 shows an enlarged sectional view of the primary parts of a low temperature tank and a fluid seal between the tank unit and the manhole cover which covers manhole at the flange joint. In the figure, 10 represents the tank unit, and 11 is the manhole cover that covers the opening of the manhole on the top surface of tank unit 10. 15 is a ring-shaped ring groove formed in the top surface of tank unit 10. The ring-shaped seal ring 30 is inserted into said ring groove 15, and it seals off the gas flowing through the fluid leakage path 16 leading into said sink tank unit
The foregoing seal ring 30 is a hollow ring with a round cross section (31 is the hollow cavity), its outside circumferential surface being in pressure contact with the outside circumferential surface 10c and bottom surface 10a of the foregoing ring groove 15, as well as with the bottom surface 11a of manhole cover 11, to thereby provide the above described gas seal.
In some cases, this low temperature tank, and the flange joint may contain very low temperature gases, approximately xe2x88x92250xc2x0 C. as described above, which causes a differential in thermal contraction to arise between seal ring 30, which exhibits high thermal contraction, and tank unit 10, which exhibits low thermal contraction, such differences can cause the seal surface variations, and the sealing to fail between said seal ring 30 and tank unit 10 manhole cover 11, resulting in a gas leak.
Further, because the foregoing seal ring 30, having a circular section, hollow-ring shape, has low resilience, when manhole cover 11 is closed over tank unit 10, said seal ring 30 is compressed against the bottom surface 10a of ring groove 15 and the bottom surface of manhole cover 11, said seal ring 30 undergoes plastic deformation, which will eventually diminish its sealing properties, to make it prone to the same kind of seal failure and gas leakage described above.
Japanese Utility Model publication (Kokai) Hei 4-117957 disclosed technology designed to deal with this problem. As is shown in FIG. 1 of the publication, the seal ring becomes a peak shape in the areas where it makes contact with the ring groove and the cover, which makes it difficult to follow the above described differences in thermal expansion. Also, the seal ring shown in FIG. 8 of the publication features a conventional, sectionally circular shaped O-ring having a wide opening at the inner circumference to form a C-shaped cross section. Since the opening is wide at the inner circumference, however, it has a low spring constant and the seal surface pressure can not be high enough, so the sealing properties are not adequate in the top and bottom sealing areas. Another seal ring having a C-shaped cross section is disclosed in FIG. 4 of Japanese patent publication (Kokai) Hei 7-208125. This type of seal ring having C-shaped cross section is, however, suitable to seal only at the outer circumference.
The present invention addresses the problems in the prior arts. The object of this invention is to provide a seal ring, and seal structure using the seal ring for flange joints used for composite tanks and pipes, that prevent seal surface variations due to differences in thermal contraction between the seal ring and the tank/the flange joint, etc., that improve the resilience of the seal, and that prevent gas leakage due to poor sealing, in order to achieve the stable sealing.
To resolve this problems, the invention provides a seal ring which fits into a ring groove formed at a joint between adjoining surfaces of first and second joint members, at least one of which is made from resin materials, to provide a tight seal to contain fluids, wherein said seal ring is provided with a heart-shaped sectional shape and a hollow cavity, and made from resilient plate materials having a greater low temperature contraction rate than the low temperature contraction rate of said resin materials. The seal ring comprises: 1) a first curved seal surface which makes contact with the bottom surface of a ring groove provided in said first joint member; 2) a second curved seal surface which makes contact with said second joint member; 3) first and second resilient curved surfaces which curve respectively from said first and second curved seal surfaces towards the inside of the hollow cavity of said heart-shaped seal ring so as to provide an indent which forms an upper portion of the heart shaped cross section of said seal ring; and 4) a pair of opposing end surfaces respectively extending from said first and second resilient curved surfaces, wherein a gap is left between said pair of opposing end surfaces.
Another preferred embodiment of this invention discloses that the gap between said pair of opposing end surfaces is formed to a dimension that allows the pressure contact of said first and second curved seal surfaces onto said opposing joint members.
Yet another preferred embodiment of this invention discloses that the seal ring provides a tight seal in below zero low temperatures, and the inner circumferences of said first and second resilient curved surfaces are structured so as to maintain contact onto the inner wall of said ring groove even during low temperature contraction.
Further, another preferred embodiment discloses a seal structure. The seal structure is used in the flange joint used for pipes, composite tanks made from composite materials such as fiber reinforced plastics, or the like made from composite materials such as fiber reinforced plastics, which contain fluids. The seal structure is used to seal a fluid sealing joint between said flange and a cover for an opening of the flange joint. The seal structure comprises: 1) a ring groove in said fluid sealing joint, into which the fluid is flowed from inside of said flange; and 2) a seal ring to be inserted into said ring groove to prevent the leakage of said fluids to the outside. The seal ring fits into a ring groove formed at a joint between adjoining surfaces of first and second joint members, at least one of which is made from resin materials, to provide a tight seal to contain fluids, wherein said seal ring is provided with a heart-shaped sectional shape and a hollow cavity, and made from resilient materials having a greater low temperature contraction rate than the low temperature contraction rate of said resin materials. The seal ring comprises: 1) a first curved seal surface which makes contact with the bottom surface of a ring groove provided in said first joint member; 2) a second curved seal surface which makes contact with said second joint member; 3) first and second resilient curved surfaces which curve respectively from said first and second curved seal surfaces towards the inside of the hollow cavity of said heart-shaped seal ring so as to provide an indent which forms an upper portion of the heart shaped cross section of said seal ring; and 4) a pair of opposing end surfaces respectively extending from said first and second resilient curved surfaces, wherein a gap is left between said pair of opposing end surfaces.
Another preferred embodiment of this invention discloses the seal structure wherein said seal ring provides a tight seal in below zero low temperatures, and the inner circumferences of said first and second resilient curved surfaces are structured so as to maintain contact onto an inner wall of said ring groove even during low temperature contraction.
According to the invention, since the hollow, sectionally heart-shaped seal ring comprised of resilient plate materials has three curved surface areas that smoothly flow together, comprised of a first curved seal surface which contacts the formed surface of the ring groove, a second curved seal surface which contacts the seal surface of a second member (e.g. manhole cover), and a projecting curved surface on the opposite side to the fluid leakage path, said seal ring, using the projecting curved surface as support points, produces spring action in the vertical direction from the elastic deformation of the first curved seal surface and the second curved seal surface, to continually press against the bottom of the ring groove for the first curved seal surface and the seal surface of the second member (manhole cover) for the second curved seal surface at a constant pressure.
Thus, even if there were seal surface variations between the seal ring and the objects being sealed which is coursed by the difference of thermal contractions, the spring action of the said seal ring causes the first curved seal surface and the second curved seal surface to maintain contact at the required pressure against their opposing seal surfaces (the seal surface of the second member and the bottom surface of the ring groove), to thereby assuredly prevent the leakage to the outside of any fluid that had flowed into the ring groove from the objects being sealed.
Further, even if slack, etc. developed in the bolts used to attached the foregoing adjoining second member and allowed some separation of the contact surfaces between the sealed member and the adjoining second member, as described above, the spring action derived from the foregoing elastic deformation, would cause the first curved seal surface and the second curved seal surface to follow that movement, and maintain continual contact with the seal surfaces at the required pressure, to thereby prevent the leakage to the outside of any fluid that had flowed into the ring groove.
Further, according to the invention, the foregoing seal ring is hollow with walls of uniform thickness and it includes five curved surfaces: the foregoing first curved seal surface, the second curved seal surface, the first curved resilient member, the second curved resilient member, and the outside curved surface, and moreover, it is equipped with an indent that passes through from the hollow to the fluid introduction side, and accordingly any fluids leaking into said hollow cavity creates internal pressure that causes the first curved seal surface and the second curved seal surface to exert more pressure against their opposing seal surfaces to thereby improve the fluid seal functions of said first curved seal surface and second curved seal surface against their opposing seal surfaces.